[STD9]     Internet Standard 9,
              <https://www.rfc-editor.org/info/std9>.
              At the time of writing, this STD comprises the following:

              Postel, J. and J. Reynolds, "File Transfer Protocol",
              STD 9, RFC 959, DOI 10.17487/RFC0959, October 1985,
              <https://www.rfc-editor.org/info/rfc959>.